1. Field of the Invention
The invention relates generally to devices and methods for filtering emboli from blood circulating within a blood vessel, and more particularly, to methods and devices for vena cava filters inserted by the femoral vein approach.
2. Description of the Prior Art
The presence of emboli within the body's circulatory system presents a serious health hazard which can often become life endangering, such as when an embolus travels into the lungs (pulmonary embolus). Most commonly, these emboli are formed in the lower extremitites, especially in patients suffering from phlebitis, patients recovering from surgery, and also non-ambulatory patients who must endure long periods of muscular inactivity. Blood clots or emboli that are formed in the lower extremities, such as the legs, must travel through the inferior vena cava in order to reach the heart, where the emboli are then pumped into the lungs becoming pulmonary embolisms.
One technique used in the prior art which served to prevent emboli from traveling into the lungs and becoming pulmonary embolisms involves the ligation of the vena cava in order to block the passage of any emboli. This technique also prevents the flow of blood through the vena cava, thus requiring the development of collateral circulation to provide passageways for satisfactory blood circulation to the heart. Because of the many disadvantages inherent in performing the major surgery required for the ligation of the vena cava, other methods have been developed.
One of these methods, disclosed in U.S. Pat. No. 3,834,394 to Hunter et al., involves a detachable balloon attached to the distal end of a catheter. The balloon and catheter are inserted by making a surgical incision in one of the veins of the neck and then using the catheter to position the balloon within the inferior vena cava. Once detached, the balloon occludes the inferior vena cava entirely, thus preventing all blood flow. While this method avoids major surgery, it still requires a surgical incision to be performed. Further, since this method also requires total occlusion of the inferior vena cava, the patient is very weak until collateral circulation eventually develops around the balloon. Hopefully, by this time, the reason for the existence of an embolism problem has past. Since this method requires the inferior vena cava to be entirely occluded, it is only used in extreme cases.
Another method for preventing pulmonary embolisms, but which does not require total occlusion of the inferior vena cava, involves implanting a filter device constructed similar to the frame of an umbrella as a permanent implant within the inferior vena cava. Such a device is disclosed in U.S. Pat. No. 3,540,431 to Mobin-Uddin. While the Mobin-Uddin device avoids total occlusion, its design does partially occlude the inferior vena cava. In addition, the Mobin-Uddin device does not avoid the disadvantages of the other previous methods in that it still requires a small incision to be made in the jugular vein and passage of the filter through the heart in order to be positioned within the inferior vena cava. This device, therefore, suffers the inherent disadvantages associated with a jugular vein approach, partial occlusion of the inferior vena cava and surgery.
Experience with devices similar to those disclosed above has demonstrated the desirability of a device which would not only serve to trap the migration of emboli but which would also not obstruct caval blood flow at any time, thus eliminating the requirement of collateral circulation. Ideally, the device should be constructed in order that it may be implanted by a femoral approach, as opposed to a more difficult jugular vein approach. Additionally, the device should not create additional emboli and should be capable of relatively secure anchoring at the desired body location within the blood vessel.
U.S. Pat. No. 3,952,747 to Kimmel discloses a blood vessel filter and filter insertion instrument which overcomes some of the disadvantages of the previous references. The Kimmel reference discloses a method which allows the filter to be inserted by a femoral approach, although this method still requires surgery in order to effect insertion. The device disclosed in the Kimmel reference uses a filter comprised of a plurality of wire legs in a generally conical array and joined at their convergent ends to an apical hub. The wire legs each include a plurality of bends intermediate along their length which decrease the solids by-pass capability of the filter without substantially occluding the blood vessel. Thus, the Kimmel reference discloses a blood clot filter which avoids the collateral circulation requirement inherent in the previous devices and the disadvantages associated with a jugular or other neck vein approach.
The filter disclosed in the Kimmel reference, however, still suffers certain disadvantages. One disadvantage, which is inherent in the conical design of the filter, is that the anchoring means must be placed at the divergent ends of the wire legs in order to securely anchor the device within the blood vessel. As a result, the divergent ends of the wire legs must be substantially collapsed and sheathed in order for the filter to be inserted within the blood vessel, and a fairly complicated means must be used to unsheath the filter for implantation within the blood vessel. Thus, the filter disclosed in the Kimmel reference inherently cannot be inserted within a blood vessel using normal percutaneous catheterization techniques. In order to use the filter disclosed in the Kimmel reference, it is necessary to perform a venotomy or incision of the blood vessel, for its insertion therein. Further, once insertion within the blood vessel is effected, a syringe type ejection means is required in order to be able to unsheath the filter for implantation.
Other references which disclose devices providing partial or total occlusion of a blood vessel in order to prevent emboli from reaching the lungs are U.S. Pat. No. 3,334,629 to Cohn and U.S. Pat. No. 3,795,246 to Sturgeon.
The device and method disclosed in the present invention overcomes the disadvantages associated with the prior art by employing a non-occlusive filter which is designed to be inserted using normal percutaneous catheterization techniques combined with a femoral approach. Thus, the need for surgery is totally obviated as well as the need for a syringe, such as disclosed in the Kimmel reference. A further improvement offered by the filter of the present invention and not found in any of the previous references involves its wire mesh design. The wire mesh design permits the filter to become firmly attached not only at the initial anchor points at the ends of the wires, but also along portions of wire length which directly abut the intimal wall of the blood vessel. The contact of the filter against the vessel wall along these portions permits endothelization and fibrotic encasement of the filter to the intimal wall surface to an extent not previously attainable using previous designs.
Accordingly, it is an object of the present invention to provide a blood clot filter which may be implanted using normal percutaneous catheter techniques combined with a femoral approach.
It is a further object of the present invention to provide a blood clot filter which is designed to be placed within the inferior vena cava, well below the renal veins.
It is a yet further object of the present invention to provide a blood clot filter which will not obstruct blood flow within the blood vessel at any time.
It is a still further object of the present invention to provide a blood clot filter which will not create additional emboli after implantation.
An additional object of the present invention to provide a blood clot filter which is capable of being securely anchored within the blood vessel.
These and other objects and advantages of the present invention will become more apparent in the following figures and detailed description.